This invention relates generally to an internal structure of a radial tire, and more specifically to a radial tire for heavy load which prevents belt edge separation.
Radial tires in general consist of a pair of right and left beads, a pair of right and left sidewalls connecting these beads and a tread disposed between the sidewalls. A carcass layer is fitted between the pair of beads and a belt layer is disposed on the tread in such a manner as to encompass the outer periphery of the carcass layer.
Steel or organic fibers such as nylon, polyester, and the like are used as the cord material for the carcass layer. Steel cords or aramide (aromatic polyamide fiber) cords are used as the cords of the belt layer.
I conventional radial tires, the cords of the carcass layer are disposed at about 90.degree. with respect to the tire circumferential direction in order to let them exhibit a hoop effect for restricting the increase of the diameter of the tread, and the cords of the belt layer are disposed in a bias arrangement at a certain angle with respect to the tire circumferential direction.
In the belt structure having such a bias laminate form, however, inter-laminar shearing stress occurs at the end portion of the belt layer in the direction of its width with the use of the tire and so-called "belt edge separation" occurs.
Various counter-measures have therefore been taken in the past. For instance, an inter-laminar gauge is increased at the end portion of the belt layer to reduce the inter-laminar shearing stress (Japanese patent application Kokai publication No. 52-22202), and the width and shape of the belt line are selected in match with the carcass line to restrict the shearing strain at the end portion of the belt layer (Japanese patent application Kokai publication No. 52-44902). However, these methods have not yet been entirely satisfactory to prevent sufficiently the belt edge separation.